Magnetic field sensing elements can be used, in a variety of applications. In one application, a magnetic field sensing element can be used to detect a direction of a magnetic field, i.e., and angle of the direction of the magnetic field.
Planar Hall elements and vertical Hall elements are known types of magnetic field sensing elements. A planar Hall element tends to be responsive to magnetic field perpendicular to a surface of a substrate on which the planar Hall element is formed. A vertical Hall element tends to be responsive to magnetic field parallel to a surface of a substrate on which the vertical Hall element is formed.
Other types of magnetic field sensing elements are known. For example, a so-called “circular vertical Hall” (CVH) sensing element, which includes a plurality of vertical Hall elements, is known and described in PCT Patent Application No. PCT/EP2008/056517, entitled “Magnetic Field Sensor for Measuring Direction of a Magnetic Field in a Plane,” filed May 28, 2008, and published in the English language as PCT Publication No. WO 2008/145662, which application and publication thereof are incorporated by reference herein in their entirety. The CVH sensing element is a circular arrangement of vertical Hall elements arranged over a common circular implant and diffusion region in a substrate. The common implant and diffusion region can be a common epi (epitaxial) region (e.g., layer) upon a substrate, bounded by semiconductor isolation structures. The CVH sensing element can be used to sense a direction (i.e., an angle) (and optionally a strength) of a magnetic field in a plane of the substrate.
Various parameters characterize the performance of magnetic field sensing elements and magnetic field sensors that use magnetic field sensing elements. These parameters include sensitivity, which is a change in an output signal of a magnetic field sensing element in response to a change of magnetic field experienced by the magnetic sensing element, and linearity, which is a degree to which the output signal of the magnetic field sensing element varies in direct proportion to the magnetic field. These parameters also include an offset, which is characterized by an output signal from the magnetic field sensing element not representative of a zero magnetic field when the magnetic field sensing element experiences a zero magnetic field.
The above-described CVH sensing element is operable, with associated circuits, to provide an output signal representative of an angle of a direction of a magnetic field. Therefore, as described below, if a magnet is disposed upon or otherwise coupled to a so-called “target object,” for example, a camshaft in an engine, the CVH sensing element can be used to provide an output signal representative of an angle of rotation of the target object.
The CVH sensing element is but one element that can provide an output signal representative of an angle of a magnetic field, i.e., an angle sensor. For example, an angle sensor can be provided from a plurality of separate vertical Hall elements or a plurality of magnetoresistance elements. Collectively, magnetic field sensing element(s) that generate an output signal related to an angle of a magnetic field are referred to herein “angle sensing elements.”
More parameters can characterize the performance of and angle sensing element(s), e.g., a CVH sensing element. One such parameter is an angular accuracy of the output signal generated by the angle sensing element(s). Angular accuracy can have both an average angle error that is the same at all magnetic field pointing angles, and also an angle error that is different at different magnetic field angles (i.e. a non-linearity error). Another parameter is the speed with which the angle sensing element(s) can convey the angle of the magnetic field. It will be understood that the speed is particularly important for applications in which the angle of the magnetic field may be rapidly changing.
It is know that some parameters that can characterize an angle sensing element tend to change with temperature.
It would be desirable to provide circuits and techniques that can process output signals from an angle sensing element to provide an output signal that has a high degree of angle accuracy and a relatively high speed.